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Every Six Weeks

It’s astounding to me, but we’ve been living rapid release for a few months now. We’re moving faster. A new feature implemented today and landed on mozilla-central can be delivered to our users in 12 to 18 weeks, not months or years. Incredibly, the same process that gives us that agility is giving us greater robustness, too. Testing and stabilization of each release across progressively larger audiences helps us find and fix bugs early, and build confidence in the quality of each release.

I want to clarify an important part of the process, though, that I think many people haven’t yet understood. Remember, an individual release train is 6 weeks of development time followed by 12 weeks of stabilization:

New work doesn’t land on Aurora and Beta. Instead, those channels focus exclusively on working with our heroic and growing community of testers to spot any unexpected issues introduced during development, and then resolve them. Looking at this diagram, you might well conclude that we’d have a release ready every 18 weeks.

Aurora and Beta are so single-minded in their focus on stabilization and testing, though, that many engineers can move on to new work. If we take a step back and look at the broader picture, this is what actually happens:

During the 12 weeks that a release spends on Aurora and Beta, the Mozilla community is not sitting idle. They are already working on features and fixes for the next release, and the release after that. Every 6 weeks their work is picked up into the next Aurora, the next Beta, and the next release. When you look at this broader picture, you notice an important point:

There can be a new release of Firefox every 6 weeks, not every 12 or 18.

I’ll say it again, because it’s important: most of the time, we’ll release a new Firefox every 6 weeks.

Many people are surprised by this fact, though it’s been part of the process all along. When Firefox 4 came out, we committed to ship the next release of Firefox within 3 months. We did it, and when we did I think many people concluded that we have moved to a 3 month cycle. In truth, though, the only reason it took us 3 months was that our Aurora and Beta channels started off empty; they had to wait for the new release to make it through the process. The next Firefox is already in Beta, and is scheduled to come out 6 weeks after the last one. When that happens, yet another Firefox will enter Beta, and so on.

We’re studying the effects of the process carefully; it’s a big change and we will be flexible in our approach as new information comes in. We may decide that 6 weeks is the wrong interval, for instance, though it’s worth remembering that Firefox maintenance releases have been released on 6-8 week intervals for years, and sometimes included major changes. We’re also paying close attention to the impacts this cycle has on our ecosystem of add-ons, plugins, and other 3rd party software that interacts with Firefox. We’re working with large organizations, too, to understand how rapid release can fit into their software deployment systems.

Whatever adjustments we make, it’s clear that rapid release is a major improvement in our ability to respond to the needs of our users and the web. Every 6 weeks we have a new Firefox to evaluate and, unless some surprising and irreconcilable breakage is discovered, release to the world. No one will have to wait a year for the developer scratchpad now in Beta, or the massive memory and performance improvements already on Aurora, or the slick tab management animations soon to land on Nightly. Rapid release is already paying dividends, and we’re just getting started.

Johnathan Nightingale
Director of Firefox Engineering

(This entry was also posted: http://blog.mozilla.org/channels/2011/07/18/every-six-weeks/)